1. Field of the Invention
The field of the invention relates to a system and method for analyzing vibration signals. More particularly, the invention relates to a system and method for analyzing vibrations signals to identify damage or manufacturing defects in vibrating devices, especially rolling element bearings.
2. Description of the Related Technology
Detection of damage and/or original manufacture defects in bearings is a significant issue for owners of certain types of large equipment. For example, bearings can be damaged by vibrations from nearby machinery. This can occur, for example, when a backup motor is stored close to a primary motor already in operation. Vibration encountered during shipping can also damage electric motor bearings. In both cases, the bearing""s rolling elements vibrate in place, breaking through the thin lubricating film separating them from the raceway. The resulting metal-to-metal contact creates wear depressions in the raceway (a condition called false brinelling). During operation, the bearing""s rolling elements pass over these depressions, causing noise and reduced bearing life.
It has been reported that improper installation is the single biggest cause of motor bearing failures. Generally, these bearings are installed manually using a dead blow hammer. If mounting force is not applied properly as the bearing is pressed into the housing, the bearing can be damaged. Other problems include using the wrong lubricant or needlessly exposing bearings to dirt and contamination.
Once integrated with a device such as a motor, it can be very expensive to shut down the device in terms of lost production or use of the device and perform diagnostics on the device to determine whether there is a problem with the bearings.
Thus, there is a need for improved method of detecting defects in devices that contain rotating elements, such as bearings. The improved system and method should allow for the accurate detection of defects without requiring direct inspection of the bearings.
One aspect of the invention comprises a method of processing vibration signal data. The method comprises collecting vibration signal data from at least one vibrating device, wherein the vibrating device includes at least a rotating inner ring, a rotating outer ring, and a plurality of rotating elements. The process then envelops the vibration signal data. Enveloping includes applying the vibration signal data to a first filter, a rectifier, and a second filter. In one embodiment, the first filter is a high pass 4th order Bessel filter having a high pass cut off frequency that is based, at least in part, upon the angular velocity of a shaft speed in the vibrating device. In one embodiment, the second filter is a 2nd order band pass filter having a band pass low cut off frequency and a band pass high cut off frequency that are each based, at least in part, upon the angular velocity of the shaft speed. The process also includes converting the vibration signal to a frequency domain signal and determining a noise floor of a frequency domain signal. The step of determining excludes a portion of the frequency domain signal that is associated with damage or original manufacture defects in the rotating inner ring, the rotating outer ring, and the plurality of rotating elements. The process also includes determining the amplitudes of selected portions of the frequency domain signal, wherein the selected portions are associated with the frequency of rotation of the rotating inner ring, the rotating outer ring, and the rotating elements, and wherein determining the amplitudes includes determining the highest amplitudes in the portions of the frequency domain signal that are respectively associated with the defects in the rotating inner ring, the rotating outer ring, and the plurality of rotating elements. The process also includes dividing the determined amplitudes of the frequency domain signal by the determined noise floor and then comparing the result of the dividing to user-definable alarm levels. A warning is displayed if the result exceeds the user-definable alarm levels.
Another aspect of the invention comprises collecting vibration signal data from at least one vibrating device, wherein the vibrating device includes at least a rotating inner ring, a rotating outer ring, and a plurality of rotating elements, enveloping the vibration signal data, converting the vibration signal data into a frequency domain signal, determining a noise floor of a frequency domain signal, determining an amplitude of selected portions of the frequency domain signal, wherein the selected portions are associated with the frequency of rotation of the rotating inner ring, the rotating outer ring, and the rotating elements, and dividing the determined amplitudes of the frequency domain signal by the determined noise floor.
Yet another aspect of the invention comprises a system including a vibration monitor that is configured to determine the standard deviation of a time domain signal that is representative the vibrations of an electronic device, the computer determining the number of times the time domain signal exceeds a threshold, wherein the threshold is based at least in part upon the standard deviation.
Yet another aspect of the invention includes a method of detecting contaminants in bearing lubrication, the method comprising measuring time domain amplitudes of noise generated by a bearing, and counting excursions in amplitude above a predefined threshold.
Yet another aspect of the invention includes a method of enveloping a vibration signal, the method comprising: receiving a vibration signal that is indicative of vibrations in a vibrating device, and applying a filter to the vibration signal, wherein the filter has a cut off frequency that is based at least in part upon the angular velocity of a rotating in the vibrating device.